Abrasion resistant laminate

ABSTRACT

A wear and gouge resistant decorative laminate is made by consolidating, under heat and pressure, a suitable backing over which lays a decor layer covered by an overlay sheet, the overlay sheet being provided on its upper surface with an ultra-thin abrasion resistant layer consistent with the disclosure of Scher et al. U.S. Pat. No. 4,255,480 and optionally O&#39;Dell et al. U.S. Pat. No. 4,499,137.

This application is a division of application Ser. No. 895,474, filedAug. 11, 1986 and now U.S. Pat. No. 5,037,694 which is acontinuation-in-part of application Ser. No. 686,350, filed Dec. 26,1984 and now U.S. Pat. No. 4,713,138.

FIELD OF INVENTION

The present invention relates to laminates and more particularly todecorative laminates having high abrasion resistance.

BACKGROUND

High pressure decorative laminates are conventionally produced bystacking and curing under heat and pressure a plurality of layers ofpaper impregnated with various synthetic thermosetting resins. In normalpractice the assembly, from the bottom up, consists of a plurality, e.g.three to eight, core sheets made from phenolic resin impregnated kraftpaper, above which lies a decor sheet impregnated with melamine resin;on top of the decor sheet is often provided an overlay sheet which, inthe laminate, is almost transparent and provides protection for thepattern sheet.

The core sheets are conventionally made from kraft paper of about 90-155pound ream weight. Prior to stacking, the kraft paper is impregnatedwith a water-alcohol solution of phenol formaldehyde resole, is driedand partially cured in a hot air oven, and is finally cut into sheets.

The decor sheet is a high quality, 50-125 pound ream weight, pigmentfilled, alpha cellulose paper that has been impregnated with awater-alcohol solution of melamine-formaldehyde resin, dried andpartially cured, and finally cut into sheets. The decor sheet, prior toimpregnation with the resin, may be printed with a decorative design, orwith a photo-gravure reproduction of natural materials, such as wood,marble, leather, etc., or it may be solid colored.

The overlay sheet was almost invariably used when the decor sheet had asurface printing in order to protect the printing from abrasive wear.The overlay sheet, a high quality alpha cellulose paper of about 15-35pounds ream weight, is also impregnated with melamine-formaldehyderesin, dried, partially cured and cut in a manner similar to that usedfor the decor sheet, except that a greater amount of resin per unitweight of paper is used.

The individual sheets are stacked in the manner indicated above and thestack of sheets is placed between polished steel plates and subjected toabout 230°-340° F. (e.g. 300° F.) at 800-1600 p.s.i. (e.g. 1000 p.s.i.)for a time sufficient to consolidate the laminate and cure the resins(e.g., about twenty-five minutes). This causes the resin in the papersheets to flow, cure and consolidate the sheets into a unitary laminatedmass referred to in the art as a decorative high-pressure laminate. Ifsix sheets of impregnated core paper are used, there results a finishedlaminate having a thickness of about 50 mils, it being understood that adifferent number of sheets can be used to provide thicker or thinnerlaminates.

In actual practice, two laminated stacks are pressed back to back,separated by a coated release sheet that allows the two laminates to bepeeled apart after separation. Also, a large proportion of the stacksare laminated with an aluminum foil-kraft paper composite sheet insertedbetween the overlay and the metal plate, with the aluminum facing theoverlay, in order to obtain a laminate having a lower gloss and aslightly textured surface which is desirable for some products.

At the completion of the laminating operation, the backs of thelaminates are sanded to permit gluing to particle board, plywood orother substrates. The glued, laminate surfaced panel is then fabricatedinto furniture, kitchen counter tops, table tops, store fixtures andother end-use applications widely accepted for the combination ofappearance, durability and economy.

A number of variations of the above-described general process are known,particularly those operations designed to obtain special effects inappearance and texture. Also other curing cycles are possible and, infact, sometimes other resin systems are used as well.

Besides decorative high-pressure laminates referred to above, there arealso a number of low-pressure products which have been developed inresent years, including low-pressure laminates using either polyesterresins, or melamine-formaldehyde resin. One of the fastest growingmaterials competing with high-pressure laminates in recent years is aproduct referred to as low-pressure melamine board which is normallypressed in a short cycle at 175-225 p.s.i. at 325°-350° F. Theselow-pressure products have the advantage of being normally lessexpensive, but they cannot be given the title of "high pressurelaminates" because a high pressure laminate product must meet a varietyof rigid standards promulgated by the National Electric ManufacturersAssociates, NEMA LD3-1980, which includes standards relating to abrasivewear, stain resistance, heat resistance, impact resistance, dimensionalstability, etc. While various other decorative surfacing materials, suchas some of the low-pressure laminates, have certain of the desirablecharacteristic, no products other than high-pressure laminates currentlyavailable have all of these properties.

One of these properties in particular which is very important isabrasion resistance. A high-pressure decorative laminate must havesufficient abrasion resistance to permit use in high exposure areas suchas dinette surface tops, check-out counters, etc. The standard NEMA testfor abrasion resistance is NEMA test LD-3.01. In this test, a laminatesample is clamped on a rotating disc, over which ride two weightedrubber wheels, faced with calibrated sand-paper strips. As the laminatesurface is rotated under the wheels, the abrasive action of the sandpaper cuts through the surface of the laminate and gradually through theoverlay until the printed pattern is exposed and destroyed. The NEMAstandard for Class I laminate requires that the laminate, after fourhundred rotation cycles, has no more than 50% of its pattern destroyed.The 50% end point is estimated by averaging the number of cycles atwhich the pattern shows initial wear, and the number of cycles at whichthe pattern is completely destroyed.

If a high-pressure decorative laminate is prepared in a conventionalmanner, with a normal 35-40% resin content in the decor sheets, butwithout an overlay sheet, the abrasion resistance will be only about50-75 cycles. If specially formulated melamine resins are used in thedecor sheet with a resin content of 50-55%, abrasion resistance of up toabout 150-200 cycles are on occasion obtainable without an overlaysheet, but in this latter case the laminates have a tendency to developsurface craze and, furthermore, they are quite difficult to prepare dueto the difficulty of impregnating the decor sheet in a uniform manner;additionally, they do not meet the 400 cycle minimum required by theNEMA standard.

Very significant improvements to the conventional system described aboveare disclosed in Scher et al., U.S. Pat. Nos. 4,255,480 and 4,263,081.These patents and their progeny disclose the production of highlyabrasion resistant laminates without overlay, the decor sheet beingcoated with a ultra-thin layer of small abrasion-resistant particles,e.g. alumina, immobilized in place on the decor sheet by a suitablebinder material, most desirably micro-crystalline cellulose. Theelimination of the overlay sheet produces very significant economicadvantages. In addition, the resultant laminates have superior abrasionresistance, meeting not only the highest NEMA abrasion resistancestandards, but also having both superior "initial wear" resistance andsuperior abrasion resistance to rubbing and sliding cans.

The emphasis in the disclosure of the Scher et al U.S. Pat. No.4,255,480 is on the economic advantages achieved by eliminating overlay,and it is pointed out at column 3 of this patent that the elimination ofoverlay saves raw material and avoids product loss attributable tohandling the overlay. The invention of the Scher et al U.S. Pat. No.4,255,480 and its progeny has been very important, even revolutionary,to the laminate art. By providing a concentrated ultra-thin layer ofabrasion-resistant particles, vastly improved wear properties have beenachieved. This has occurred without diminution of other necessary andrequired laminate characteristics, including resistance to heat,resistance to stain by common household chemical and foods, resistanceto impact and resistance to boiling water, all consistent with the NEMALD3-1980 standards.

More recently, a further improvement has been provided according to theO'Dell et al U.S. Pat. No. 4,567,087 by which the abrasion resistantsurface according to Scher et al U.S. Pat. No. 4,255,480 is also madescuff resistant by the inclusion of solid lubricant. O'Dell et al U.S.Pat. No. 4,499,137 also relates to scuff resistant laminates.

More recently, a new process has been developed for producing suchabrasion-resistant decorative laminate in a more economical fashion. Thenew process, set forth in the Ungar et al U.S. application Ser. No.686,350, involves substantially simultaneously applying the ultra-thincoating while impregnating the decor paper.

In spite of these remarkable and important improvements as outlinedabove and disclosed in Scher et al U.S. Pat. No. 4,255,480, O'Dell et alU.S. Pat. No. 4,567,087 and Ungar et al Ser. No. 686,350, now U.S. Pat.No. 4,713,138 there are still occasions when a different type ofapproach is desirable. For example, in the manufacture of laminatesintended for use in flooring, the laminate surface is exposed to atremendous amount of wear. Even though the improvements of Scher et al,O'Dell et al and Ungar et al provide vastly improved wear resistance,these environments, such as for flooring, need even greater wearresistance.

Other problem areas are certain high abuse applications, where it isnecessary that the surface not only resist wearing and scuffing, butalso gouging. As the ultra-thin abrasion resistant coating of Scher etal and O'Dell et al is ultra-thin, under some unusual circumstances itmay lack resistance to cutting or gouging. Once the surface is broken,the decor layer, especially if surface printed, may be gouged away andcontrasting base paper exposed. Printing ink layers are very thin and inaddition, printing is often on a contrasting paper which easily showsany breaks in the ink layer.

Another problem can occur in the manufacturing process. In spite of theimprovements of Ungar et al Ser. No. 686,350, there are certain designswhich are quite expensive to produce because they are run in such smallquantities, e.g. for custom design purposes. It would be economicallyadvantageous if the highly abrasion resistant products of Scher et aland O'Dell et al could be made without the processing in separate runsof small quantities of specially designed decor sheets.

SUMMARY

It is, accordingly, an object of the present invention to provide alaminate product having not only superior abrasion resistance consistentwith the product of Scher et al U.S. Pat. No. 4,255,480, and optionallysuperior scuff resistance consistent with the products of O'Dell et alU.S. Pat. Nos. 4,567,087 and 4,499,137, but which also has superiorgouge resistance.

It is another object to provide for improved decorative laminatescapable of withstanding extraordinary conditions of wear, such as inflooring environments.

It is a further object of the present invention to provide for lesscostly decorative laminates having unusual decor sheets by simplifyingthe handling operations during their manufacture.

These and other objects of the invention are achieved according to theprocess of Ungar et al U.S. application Ser. No. 686,350, the contentsof which are incorporated herein by reference, applied to overlay paperinstead of to decor paper, followed by assembling in a stack from thetop down the overlay paper provided with an ultra-thin abrasionresistant layer according to Ungar et al Ser. No. 686,350, a decor sheetand a plurality of core sheets. The assembly is then subjected tolamination under heat and pressure using conventional laminatingconditions, and there is thus produced a decorative laminate havingincreased wear resistance and gouge resistance.

DETAILED DESCRIPTION OF EMBODIMENTS

According to a preferred procedure, high pressure decorative laminate ismade according to the process of Ungar et al Ser. No. 686,350, exceptthat the ultra-thin abrasion resistant composition optionally containingwax particles is applied to conventional overlay paper. The paper ispartially cured to the B-stage in a standard fashion. The so-obtainedoverlay paper is assembled with conventional decor paper therebeneath,below which are provided a plurality of core sheets. After laminating at800-1200 psi and 265°-305° F., a high pressure decorative laminate isobtained having superior abrasion, scuff and gouge resistance. As theultra-thin abrasion and scuff resistant coating is thin, clarity of thepattern of the decor paper is not severely disturbed.

In making decorative laminates having unusual patterns, e.g. customruns, the present invention simplifies the processing considerably. Ifit is necessary to provide the abrasion resistant ultra-thin coatingdirectly onto the decor sheet, then the coating and impregnating machinemust be stopped each time there is a change in the decor paper. Whenthis happens frequently, costly shut-down time increases. However,according to the present invention this problem is obviated by providingthe ultra-thin abrasion resistant coating onto overlay paper, and thesame overlay paper is used regardless of the nature of the decor paper,and even where perhaps only a few sheets of each of many differentspecial types of patterns or decors are used; consequently shutdown timeis reduced.

The following examples, offered illustratively, will further illustratethe invention.

EXAMPLE I

A laminating resin/abrasion resistant coating composition according toUngar et al Ser. No. 686,350 was prepared by adding with stirring 156parts by weight of water to 533 parts of melamine-formaldehyde resin(62% concentration), followed by mixing therewith 0.39 parts ofsurfactant (Triton CF-21), 0.27 parts of polyethylene glycolanti-foaming agent (Emerest 2652), and 1.1 parts of polyethylene wax(Shamrock PE 394). Next were added 11.1 parts of 30 micron aluminumoxide (WCA 30) at low shear mixing. Lastly there were added 8 parts ofmicrocrystalline cellulose (Avicel RC 591) while mixing at high shearfor two minutes.

While any laminating resin can be used, a melamine resin was used inthis example having a 2-3 F/M mole ration and a water tolerance of 2-3.The stirring or mixing was carried out using a propeller blade;alternatively, a Cowles Dissolver can be used as well as other types ofmixers. The viscosity of the composition was then adjusted to permitcoating to about 186 cps at 80° F. using a Brookfield #2 spindle.Increasing the quantity of Avicel increases the viscosity, anddecreasing the amount of Avicel decreases the viscosity.

The composition was then coated on 30 pounds per ream alpha celluloseoverlay paper in an amount sufficient to give a 65% pickup, therebyimpregnating the overlay paper to provide 50.8 pounds of melamine solidsand 4.4 pounds volatile per ream, as well as an ultra-thin abrasionresistant coating having 1.68 pounds of alumina, 1.22 pounds ofmicrocrystaline cellulose and 0.16 pounds of wax per ream.

The so-produced dried and B-staged overlay was laminated over normaldecorative print paper saturated with melamine in the usual way, itselfoverlaying a plurality of phenolic impregnated core layers also preparedin the normal way. The resultant laminate met all NEMA properties exceptthat initial wear was 1600 cycles instead of 275-375 cycles.

EXAMPLE II

Two additional runs similar to Example I were carried out except in onecase 5.5 parts by weight of aluminum oxide were added to thecoating/impregnating composition, and in the second case 22 parts byweight of aluminum oxide were used. Samples from Example I and the tworuns of Example II were comparatively tested for initial wear. Theresults are shown in Table A below.

                  TABLE A                                                         ______________________________________                                        Aluminum Oxide  Initial Wear                                                  #/Ream          Cycles                                                        ______________________________________                                        0.85            1150                                                          1.68            1550                                                          3.27            2575                                                          ______________________________________                                    

When these results are plotted, they show a generally direct linearrelationship between the quantity of aluminum oxide and the initial wearin cycles; however, if these figures are plotted and extrapolated backto zero alumina, the plot shows an initial wear in cycles of about 550cycles which is a little higher than 325-400 cycles actuallyexperienced.

The other properties of the samples tested were well within NEMAstandards.

EXAMPLE III

Example II was repeated five times using in each case 1.68 pounds perream of aluminum oxide WCA 30 microns. In each case a different patternpaper was used as identified in Table B below. For each run according tothe present invention, there was also conducted a control run usingoverlay without the ultra-thin abrasion resistant coating. Afterproduction of the samples, they were comparatively tested for initialwear, the results being as shown in Table B below:

                  TABLE B                                                         ______________________________________                                                     Initial Wear Cycles                                              Pattern        Invention                                                                              Control                                               ______________________________________                                        W-8-94         1694     469                                                   AN-2-2         1600     350                                                   AR-2-1         1525     400                                                   LH-7-1         1525     475                                                   W-8-252        1600     375                                                   ______________________________________                                    

In all five comparisons, laminates according to the present inventionprovided at least three times the abrasion resistance compared to theircontrols, as measured by the NEMA initial wear test. Inclusion of thesolid wax particles gave superior scuff resistance. The added thicknessprovided by the overlay produced laminates having superior gougeresistance.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and therefore such adaptations and modifications are intended to becomprehended within the meaning and range of equivalents of thedisclosed embodiments. It is to be understood that the phraseology orterminology employed herein is for the purpose of description and not oflimitation.

What is claimed is:
 1. A wear and gouge resistant decorative laminatecomprising a backing layer and laminated thereto a thermoset laminatingresin impregnated decor sheet, said decor sheet having laminated to theupper surface thereof an overlay sheet having on its upper surface anultra-thin abrasion resistant coating, said ultra-thin abrasionresistant coating having a thickness of up to about 0.3 mils andcomprising a mixture of (1) and abrasion resistant hard mineral of sizeand quantity sufficient to provide for abrasion resistance withoutinterfering with visibility and (2) stabilizing binder material for saidmineral, said thermoset resin being impregnated throughout said decorlayer and said overlay sheet and said ultra-thin coating, said bindermaterial not interfering with visibility, and with said ultra-thinabrasion resistant coating forming the uppermost layer of said laminate.2. A decorative laminate in accordance with claim 1, wherein saidultra-thin layer further comprises a solid lubricant in an amountsufficient to provide good scuff resistance.
 3. A decorative laminate inaccordance with claim 1, wherein said thermoset resin ismelamine-formaldehyde resin or polyester resin.
 4. A decorative laminatein accordance with claim 1, wherein said ultra-thin coating has acalculated thickness of about 0.05-0.3 mils.
 5. A decorative laminate inaccordance with claim 1, wherein said binder material comprisespredominantly microcrystalline cellulose.
 6. A decorative laminate inaccordance with claim 1, wherein said abrasion resistant mineralparticles constitute alumina, silica or mixtures thereof.